tyrphostin-ag825 and Prostatic-Neoplasms

Androgen ablation therapy is the most common strategy for suppressing prostate cancer progression; however, tumor cells eventually escape androgen dependence and progress to an androgen-independent phase. The androgen receptor (AR) plays a pivotal role in this transition. To address this transition mystery in prostate cancer, we established an androgen-independent prostate cancer cell line (LNCaPdcc), by long-term screening of LNCaP cells in androgen-deprived conditions, to investigate changes of molecular mechanisms before and after androgen withdrawal. We found that LNCaPdcc cells displayed a neuroendocrine morphology, less aggressive growth, and lower expression levels of cell cycle-related factors, although the cell cycle distribution was similar to parental LNCaP cells. Notably, higher protein expression of AR, phospho-Ser(81)-AR, and PSA in LNCaPdcc cells were observed. The nuclear distribution and protein stability of AR increased in LNCaPdcc cells. In addition, cell proliferation results exhibited the biphasic nature of the androgen (R1881) effect in two cell lines. On the other hand, LNCaPdcc cells expressed higher levels of Her2, phospho-Tyr(1221/1222)-Her2, ErbB3, and ErbB4 proteins than parental LNCaP cells. These two cell lines exhibited distinct responses to Her2 activation (by heregulin treatment) on Her2 phosphorylation and Her2 inhibition (by AG825 or Herceptin treatments) on proliferation. In addition, the Her2 inhibitor more effectively caused AR degradation and diminished AR Ser(81) phosphorylation in LNCaPdcc cells. Taken together, our data demonstrate that Her2 plays an important role in the support of AR protein stability in the transition of androgen requirement in prostate cancer cells. We hope these findings will provide novel insight into the treatment of hormone-refractory prostate cancer.

Topics: Androgens; Antibodies, Monoclonal; Antibodies, Monoclonal, Humanized; Antineoplastic Agents; Benzothiazoles; Blotting, Western; Cell Cycle; Cell Line; Cell Survival; Cells, Cultured; Humans; Male; Metribolone; Prostatic Neoplasms; Protein-Tyrosine Kinases; Receptor, ErbB-2; Receptors, Androgen; Trastuzumab; Trypan Blue; Tyrphostins

We examined the efficacy of combination treatments utilizing cytotoxic drugs plus inhibitors to members of the ErbB-ERK signal pathway in human prostate cancer (PCa) LNCaP C-81 cells. Under an androgen-reduced condition, 50nM gemcitabine caused about 40% growth suppression on C-81 cells. Simultaneous treatment of gemcitabine plus 10microM AG825 produced 60% suppression (p<0.03); while, 85% growth inhibition (p<0.02) was seen if AG825 was added to gemcitabine-treated cells after a 24h-interval. Our data thus showed that in androgen-reduced conditions, inhibition of ErbB-2 increases the cytotoxic efficacy of gemcitabine in PCa cells. This finding has significant implications in the choice of drugs for combination therapy as well as the order of administration for treating cancer patients.

Topics: Androgens; Antimetabolites, Antineoplastic; Antineoplastic Combined Chemotherapy Protocols; Apoptosis; bcl-2-Associated X Protein; bcl-X Protein; Benzothiazoles; Cell Line, Tumor; Cell Proliferation; Deoxycytidine; Dose-Response Relationship, Drug; Down-Regulation; Extracellular Signal-Regulated MAP Kinases; Flavonoids; Gemcitabine; Humans; Male; Prostatic Neoplasms; Protein Kinase Inhibitors; Proto-Oncogene Proteins c-bcl-2; Quinazolines; Receptor, ErbB-2; Time Factors; Tyrphostins

Prostate cancer (PCa) progression is aided by abnormal autocrine growth factor loops. We screened for small cell-permeable inhibitors of receptor tyrosine kinases that could block their signaling and trigger cell death in PCa cell lines. We found that the human epidermal growth factor receptor (HER)-2/neu inhibitor tyrphostin AG825 is preferentially toxic to PCa cells that are phenotypically androgen independent. These effects were dose and time dependent in the human LNCaP, C4, and C4-2 cell line models of progression and correlated with the inhibition of HER-2/neu phosphoactivation and its down-regulation. In addition, we show that the inhibition of HER-2/neu signaling with AG825 triggers an imbalance between extracellular signal-regulated kinase 1/2 and p38 mitogen-activated protein kinase activation, which leads to p38-dependent apoptosis. Inhibition of HER-1 with Compound 56 had no effect. These findings suggest that the androgen-independent C4 and C4-2 cells can be killed by selectively inhibiting their HER-2/neu signaling pathway and provide insights into the mechanism of action of AG825 in PCa cells.

Topics: Androgens; Apoptosis; Benzothiazoles; Enzyme Activation; Enzyme Inhibitors; ErbB Receptors; Humans; Male; Mitogen-Activated Protein Kinase 1; Mitogen-Activated Protein Kinase 3; Mitogen-Activated Protein Kinases; Neoplasms, Hormone-Dependent; p38 Mitogen-Activated Protein Kinases; Prostatic Neoplasms; Protein Serine-Threonine Kinases; Proto-Oncogene Proteins; Proto-Oncogene Proteins c-akt; Receptor, ErbB-2; Signal Transduction; Tumor Cells, Cultured; Tyrphostins